The present application is based on and claims priority from the following Japanese Patent Applications: 2001-116680, filed Apr. 16, 2001; 2001-116681, filed Apr. 16, 2001; and 2001-116682, filed Apr. 16, 2001; the content of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a battery charging system that includes a vehicle generator mounted in a vehicle, such as a passenger car or a truck.
2. Description of the Related Art
Recently, the idling speed of vehicle engines has been lowered, while vehicle electric loads are increased. In order to cope with the above-stated tendency, it has been proposed that the output voltage of generators is controlled according to various conditions such as vehicle running condition, engine operating condition, battery charge condition, electric load condition or the like. JP-B2-3070788 discloses such a generator control unit, in which a duty ratio signal that corresponds to a target voltage is provided by an ECU to control an IC regulator, thereby regulating the output voltage of a vehicle generator according to various vehicle conditions.
For example, the output voltage is controlled to be lower to reduce the output power of the generator, such as 12 V, when the vehicle is accelerated, thereby reducing fuel consumption. On the other hand, the output voltage is controlled to be higher to increase the output power of the generator, such as 15 V, when the vehicle is decelerated, thereby increasing the amount of electric energy to be charged to a battery.
When an engine is started by a starter at a cold temperature, a catalyst may not be fully activated if the torque of the vehicle generator in operation becomes too much for the engine. As a result, a considerable amount of unburned fuel may be discharged just after the engine is started, especially at a very low temperature. If the output voltage of the vehicle generator is lowered by the generator control unit according to the disclosure of the above publication during engine is being started, it is difficult to control the output power of the generator because a large amount of battery current is supplied to the starter and the terminal voltage of the battery becomes very low.
In order to start the engine even in the above condition, a specific circuit for limiting the output power of the vehicle generator may be mounted in the vehicle generator. However, such a specific circuit limits the output power of the vehicle generator although ambient temperature or engine coolant temperature is high enough for the engine start operation. This may unnecessarily reduce the engine load even at a normal temperature, thereby causing racing of the engine that may annoy a driver.
Further, although the target voltage is set to a maximum voltage, the output voltage changes from 16 V to 14.4 V if the duty ratio changes a little higher. Therefore, it is necessary to detect the temperature of the battery in order to accurately control the output voltage. That is, a specific temperature sensor has to be mounted where the battery temperature can be detected.
The generator control system disclosed in JP-B2-3070788 gradually increases the output power of the vehicle generator to prevent the engine operation from becoming unstable. However, if the output voltage of the vehicle generator is intended to increase when the vehicle is decelerated, in order to convert the kinetic energy of the vehicle into electric power to be charged to the battery 3, such a generator control system may hamper such energy recovery.
Therefore, the present invention has been made in view of the above problems.
It is a main object of the invention to provide an improved battery charging system and a generator control unit for an automotive vehicle that ensure complete engine starting, reduce fuel consumption of the engine of the vehicle and prevent the fuel from being unburned.
Another object of the invention is to provide an improved generator control unit of the above-stated battery charging system.
In a battery charging system that is used with a generator according to a main feature of the invention, a generator control unit is comprised of a duty-ratio detecting means for detecting a duty ratio of a command pulse signal, an output power limiting circuit for limiting the output power of the generator, a voltage regulator for regulating the output voltage of the generator to a voltage proportional to the duty-ratio of the command pulse signal and activation means for activating the output power limiting circuit to limit the output power of the generator when the duty-ratio falls within a predetermined range.
Accordingly, a vehicle engine can be started under such an excellent condition that fuel consumption can be reduced and, also, unburned fuel can be prevented from discharging from the vehicle engine. Moreover, it is not necessary to provide two kinds of power control units for limiting generator""s output power.
It is preferable that the predetermined range includes a duty-ratio at which the output voltage is regulated to be minimum. It is also preferable that the generator control unit includes a generator rotation speed detecting circuit. With the generator rotation speed detecting circuit, the activation means activates the output power limiting circuit to limit output power of the generator if the duty ratio falls in the predetermined ratio range and in a predetermined speed range.
It is preferable that the output power is limited by limiting field current supplied to the field coil of the vehicle generator. For this purpose, the voltage regulator may include a power transistor for controlling the field current. Preferably, the output power limiting circuit controls the output power by controlling conduction ratio of the power transistor. The output power limiting circuit may also limit the peak voltage of one of the phase winding within battery voltage when the battery is disconnected or when the engine is started by a starter.
Preferably, the generator control unit includes a load responsive control unit for limiting the field current when the generator is connected to an electric load and when the activation means switches the output power limiting circuit from its activating state to deactivating state.
Another object of the invention is to provide an improved battery charging system that does not necessitate a specific hardware for transmitting the command pulse signal.
In a battery charging system having a generator control unit according to another feature of the invention, the generator control unit is comprised of a duty-ratio detecting means for detecting a duty ratio of a command pulse signal transmitted from outside, a reference voltage generating means for providing reference voltage that is approximately proportional to the duty-ratio between a maximum value and a minimum value of the duty ratio and is fixed at one of the maximum and minimum values, and a voltage regulator including means for comparing the reference voltage with terminal voltage of a battery.
The reference voltage generating means is preferably disposed where ambient temperature changes relative to temperature of the battery so that the reference voltage can be set according to the ambient temperature when the duty-ratio is in a range near the maximum value or the minimum value.
It is preferable that an outside control unit (ECU) for generating the command pulse signal is comprised of a CPU for calculating the duty-ratio of the command pulse signal according to at least one of a battery charge condition, a vehicle speed and a throttle valve position in synchronism with a clock signal, a pulse signal generator including a switching circuit and a register for holding on-off state of the switching circuit. Thus, content of the register is changed by the means for calculating a duty-ratio in synchronism with said clock signal to change said on-off state of said switching circuit, thereby generating said command pulse signal.
It is also preferable that the command pulse signal has a cycle time that is a multiple of a cycle time of the clock signal and is shorter than a time constant of the vehicle generator.
It is also preferable that the reference voltage generating means is disposed where ambient temperature changes relative to temperature of the battery so that the reference voltage can be set according to the ambient temperature when the duty-ratio is in a predetermined range. In this case, the CPU sets a duty-ratio of the command pulse signal at a minimum value so that the reference voltage can be minimum when detected that the vehicle is accelerated, to a maximum value so that the reference voltage can be maximum when detected that the vehicle is decelerated and to a value in the predetermined range when detected that the vehicle is not accelerated or decelerated and that the battery is in a state of being charged.
Another object of the invention is to provide an improved battery charging system and generator control unit that are effective to stabilize engine operation and to reduce fuel consumption of the engine.
In a battery charging system including a generator control unit according to another feature of the invention, the generator control unit is comprised of a duty-ratio detecting means for detecting a duty-ratio of a command pulse signal, a load responsive control circuit for limiting increase of current supplied to the field coil of the generator, a voltage regulator for controlling output voltage of the generator to be proportional to the duty-ratio and means for disabling the load responsive control circuit from controlling voltage increase if the duty ratio is in a predetermined range.
Therefore, the output power can be controlled both for stabilizing rotation of the engine and for converting kinetic energy of the vehicle into electric energy to be charged into a battery.
It is preferable that the predetermined range includes a duty-ratio that makes the voltage regulator control the output voltage of the generator at a maximum voltage (e.g. 15 V).
An outside control unit (ECU) for generating the command pulse signal may be comprised of a CPU for calculating the duty-ratio of the command pulse signal according to one of a battery charge condition, such as a vehicle speed or a throttle valve position, and a pulse signal generator including a switching circuit and a register for holding on-off state of the switching circuit. The content of the register is changed in synchronism with the clock signal, so that the on-off state of the switching circuit is changed to generate the command pulse signal. It is preferable that the command pulse signal has a cycle time that is a multiple of a cycle time of the clock signal and is shorter than a time constant of the vehicle generator.